In order to improve the coverage rate of high-speed data rate service and the average throughput of the point edge and the point, the coordinated multi-point transmission/reception (COMP) technology is introduced into the LTE-A system.
In the current LTE-A, the COMP technology is mainly divided into two types as follows: (1) joint transmission technology: each point in the coordinated transmission set can obtain the data information, and the physical downlink shared channel (PDSCH) data are transmitted through multiple points or one point at the same time; and (2) coordination scheduling: only the serving point can obtain the data information to be transmitted, but the confirmation for the user scheduling and the shaped-beam is accomplished through the consultation in coordination set.
In order to support the downlink COMP transmission above, three feedback mechanisms below are considered in the current LTE-A: (1) the feedback of explicit channel state/statistical information: the channel information is same as the information observed by the receiving side and is not transmitted or processed by the receiver; (2) the feedback of implicit channel state/statistical information: different transmission or reception processing mechanisms are utilized for the feedback, e.g. the feedback of pre-coding matrix indicator (PMI), channel quality indicator (CQI) and rank indicator (RI) information; and (3) the utilization of channel mutual benefits: the sounding reference signal (SRS, used for the estimation of uplink channel at the network side) transmitted uplink by the user equipment (UE) is used for the estimation of downlink channel information.
In the COMP, the coordinated transmission set is the subset of the COMP measurement set and is determined by the network side (such as eNodeB). If the UE only feeds back the independent CQI value of each point, the eNodeB cannot calculate the practical CQI value accurately during the coordinated transmission according to each independent CQI value. If the UE also feeds back each combined CQI value besides independent CQI value of each point, the overhead is too large. If the UE only feeds back one joint CQI value, the network side cannot obtain the accurate CQI value when the coordinated transmission set is inconsistent with the COMP measurement set.